Didactic

Something is didactic if it consciously and demonstrably sets out to teach a lesson. For example, many U.S. sitcoms aimed at younger viewers have theme episodes where they take a moral stance on an issue like drug use eating disorders. Also, I remember (with some fondness, I'm afraid I have to admit), the Highlights for Children comic strip Goofus and Gallant's etiquette lessons like the one below.

Also, check out this funny (very unpolitically correct) parody of Goofus and Gallant.